It will be appreciated by those having ordinary skill in the art that cellulose crosslinking is an important textile chemical process that forms the basis for an array of finished textile products. Previous efforts involving ionic crosslinking do not allude to imparting durable press performance, stability, and strength to the substrate. See Ungefug, G. A. and Sello, S. B., Textile Chemist and Colorist, 15(10) 193 (1983). In contrast, the presently disclosed subject matter shows that many desirable mechanical stability properties, such as crease resistance, anti-curl, shrinkage resistance, and durable press, can be imparted to a cellulosic material, such as cotton, by the application of ionic crosslinks. Formaldehyde-based N-methylol crosslinkers are commonly used to impart many of the above-mentioned mechanical stability properties to a cellulosic material, but also give rise to strength loss and the potential to release airborne formaldehyde, a known human carcinogen. See Peterson, H., Cross-Linking with Formaldehyde-Containing Reactants, in Functional Finishes, Vol. II, Part B (Lewis, M. and Sello, S. B., eds., Dekker, New York, 1983), p. 200. Other non-formaldehyde systems, e.g., polycarboxylic acids, have been tested with varying degrees of success. See Yang, C., et al., Textile Res. J., 68(5), 457 (1998); Yang, C. et al., Textile Res. J., 70(3), 230 (2000). The limited success of these systems results from difficulties due to high cost, requirements for stringent processing conditions, and use of exotic catalysts. Accordingly, there is a need for a low-cost, simple process for producing crosslinks in a cellulosic material that gives the material desirable mechanical stability properties, e.g., crease angle recovery performance, without the potential for releasing low molecular weight reactive materials, such as formaldehyde. This need is fulfilled by the ionic crosslinking method described herein by the presently disclosed subject matter.
One possible route to ionic crosslinks involves cationized chitosan (CC), a water-soluble polycation (i.e., a polyelectrolyte) with a high degree of cationization. There are other possible routes to ionic crosslinks that involve other polyelectrolytes. For example, Kim et al. have produced cationized chitosan by using glycidyl trimethylammonium chloride. See Kim, Y., et al., Textile Res. J., 68(6), 428 (1998). The method of cationizing chitosan used by Kim et al., however, produces a cationized chitosan that is substituted at the ring NH2 site, thereby reducing its reactivity and limiting its degree of cationization. Accordingly, there is a need for a process for producing a cationized chitosan in which the substitution of the chitosan is directed toward the C6 and ring hydroxyl sites, thereby allowing a higher degree of cationization and preserving the ring NH2 sites with their associated reactivity.
Additionally, desirable properties can be imparted to a cellulosic material when the material is reacted with a cationizing agent, such as 3-chloro-2-hydroxypropyl trimethyl ammonium chloride (CHTAC) or epoxypropyl trimethyl ammonium chloride (EPTAC), thus rendering it cationic in nature. See Hashem, M., et al., Textile Res. J., 73(11), 1017(2003); Hauser P., et al., AATCC Review, 2(5), 36 (May, 2002); Hauser. P. et al., Color Technol., 117(5), 284 (2001); Hauser, P., Textile Chemist and Colorist & American Dyestuff Reporter, 32(6), 44, (June 2000); Hauser. P., et al., Textile Chemist and Colorist & American Dyestuff Reporter, 32(2), 30 (February 2002); Draper, S. et al., AATCC Review, 2(10), 24 (October 2002); Draper, S., et al., AATCC International Conference and Exhibition Book of Papers, AATCC, Research Triangle Park, NC (Oct. 3, 2002). An important factor in the economic feasibility of such treatments is the efficiency of the utilization of cationizing agent, e.g., CHTAC or EPTAC. Typically, the utilization efficiency of the cationizing agent is less than 100% due to the competing hydrolysis reaction as illustrated for CHTAC in Scheme 1.

Referring now to Scheme 1, the reaction of CHTAC occurs in two steps. First, the CHTAC is rapidly converted to EPTAC by Reaction I. The EPTAC subsequently reacts more slowly with either water to form a hydrolyzed waste material by Reaction II, or with cellulose or chitosan to form cationized cellulose or cationized chitosan, respectively, by Reaction III. The waste of reactant materials by Reaction II is undesirable and increases the cost of the cationization process and the effluent pollution load. Accordingly, there is a need for improving the efficiency of the process for cationizing cellulosic materials, such as cotton.